Sliding cam system having an extended engagement region

ABSTRACT

A sliding cam system, having at least one sliding cam, which is arranged in a rotationally fixed but axially displaceable manner on at least one axially fixed base shaft of a reciprocating-piston internal combustion engine in order to form a camshaft, at least one actuating device for moving the sliding cam into different axial positions by at least one actuating pin that can reach into at least one displacement groove on the periphery of the sliding cam. The actuating device has a machine-fixed housing and the displacement groove is formed in a top circle surface of the sliding cam down to a groove base and is helical and has an insertion region, a displacement region having an accelerating flank and a braking flank, and a retraction region for the actuating pin. An extended engagement region is associated with the displacement groove and the extended engagement region at least partially has a material removal from the level of the top circle surface in the direction of the groove base.

BACKGROUND

The invention relates to a sliding cam system, having at least one sliding cam, which is arranged in a manner which prevents relative rotation but allows axial shifting on at least one axially fixed base shaft of a reciprocating-piston internal combustion engine in order to form a camshaft, having at least one actuating device for adjusting the sliding cam into different axial positions by at least one actuating pin that can be made to engage in at least one shifting groove on the periphery of the sliding cam, wherein the actuating device has a housing fixed to the engine and the shifting groove is machined into a top circle surface of the sliding cam down to a groove bottom and is of helical design and has an entry region, a shifting region having an accelerating flank and a braking flank, and an exit region for the actuating pin.

A sliding cam system of this kind, corresponding to the preamble, is known from DE 10 2009 009 080 A1. Two shifting grooves are arranged in series on the top circle surface of the sliding cams of this system, said grooves having cam tracks extending axially in opposite directions on the periphery of the top circle surface and being designed as double S grooves. Under unfavorable operating conditions, e.g. at a high switching speed and a low temperature, the exit speed of the respective actuating pin from the housing can be too low to engage correctly in the respective shifting groove. This can lead to incorrect switching, incorrect positioning and partial overlaps.

SUMMARY

It is the object of the invention to improve a sliding cam system of the type corresponding to the introduction in such a way that the disadvantages mentioned are eliminated. The intention is to ensure that incorrect switching, incorrect positioning and partial overlaps do not occur and that reliable and precise shifting of the sliding cam takes place under all operating conditions.

According to the invention, this object is achieved by virtue of the fact that the shifting groove is assigned an extended engagement region and that the extended engagement region at least partially has a material removal from the level of the top circle or top circle surface in the direction of the groove bottom. The extension of the engagement region essentially follows the entry region, counter to the direction of rotation of the sliding cam. This ensures that the actuating pin can already exit completely from the actuating device in this region without being hindered by top circle regions. High exit speeds of the actuating pin are therefore not required, with the result that slow, simple and low-cost actuating devices can be used. Each shifting groove is advantageously assigned an extended engagement region, allowing the proposed measures also to be used for both grooves of a double S groove.

The material removal is embodied in such a way that it extends as far as the level of the groove bottom and has the same peripheral extent as the extended engagement region.

In another embodiment of the invention, it is provided that, in the case of a double S groove system having two shifting grooves, the extended shifting region and the material removal for the first shifting groove is between about 145° and about 290° of cam angle and the extended engagement region for the second shifting groove amounts to about 75° to about 290° of cam angle. This results in a significant improvement in the possibility for entry and the entry distance of the respective actuating pin. The extended engagement region having a material removal can correspond to the complete sliding cam periphery minus the shifting region, thus ensuring that long peripheral distances are available for the entry of the actuating pins.

Since the braking flank is partially cut away, depending on the embodiment of the extended engagement region, it is provided that the braking flank of the shifting region is offset outward into the wall of the shifting groove.

Since a retaining device, which has a spring-loaded retaining element that is in operative connection with a respective retaining recess assigned to each of the axial positions, is generally effective on the sliding cam, the retaining device can also be used to contribute to the braking of the sliding cam in the respective shifted position.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in the drawings:

FIG. 1 shows a dual diagram showing a development of the periphery over 900° of cam angle, wherein the shifting of the sliding cam is plotted in the upper half and the groove bottom depth is plotted in the lower part;

FIGS. 2, 3 and 4 each show a view of a top circle region and sections through the latter for a first groove arrangement;

FIGS. 5, 6 and 7 each show a view of a top circle region and sections through the latter for a modified groove arrangement, and

FIGS. 8 and 9 show views of top circle regions of sliding cams for modified groove arrangements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 to 9, where shown individually, 1 denotes the shifting path of a sliding cam in one direction and 2 denotes the shifting path of the sliding cam in the opposite direction. 3 a denotes the entry distance of an actuating pin, which leads at the end to the shifting of the sliding cam along the shifting path 1. The entry distance 3 a of the actuating pin relates to the first shifting groove. A corresponding entry distance for a second shifting groove, denoted by 3 b, begins at about 270° of cam angle and ends at about 560° of cam angle.

In FIG. 2, which shows a top circle region, the top circle surface is denoted by 4. Arranged adjacent thereto is a shifting groove, which is denoted by 5. Section E-E in FIG. 4 passes through the shifting groove 5 and shows that a large extended engagement region, denoted by 9, is provided, into which a material removal is machined as far as a groove bottom 7. The extended engagement region 9 comprises a cam angle of somewhat more than 145°. Section D-D shown in FIG. 3, which passes through the shifting groove 6 and the top circle surface 4, shows an extended engagement region 10, which amounts to about 75° of cam angle. The material removal as far as a groove bottom 8 is embodied in a corresponding manner.

The view of the top circle surface 4 in FIG. 5 shows a modified embodiment of the double S groove, wherein the shifting groove denoted by 5 a and the shifting groove with the reference sign 6 a can be seen. As is apparent from FIG. 7, the extended engagement region 11 of shifting groove 5 a amounts to more than about 290° of cam angle and the extended engagement region 12 of shifting groove 6 a likewise to more than about 290° of cam angle.

Modified double S grooves are once again shown in FIGS. 8 and 9 together with the top circle surfaces 4. In the case of shifting groove 5 a, a braking flank offset 13 is provided and, in the case of shifting groove 6 a, a braking flank offset 14 is provided, these being machined into the wall of the shifting groove since the braking flanks that are normally present in the absence of the inventive features are removed.

LIST OF REFERENCE NUMBERS

-   1) shifting path of the sliding cam -   2) shifting path of the sliding cam -   3) entry distance of the actuating pin -   4) top circle surface -   5) shifting groove -   5 a) modified shifting groove -   6) shifting groove -   6 a) modified shifting groove -   7) groove bottom -   8) groove bottom -   9) extended engagement region -   10) extended engagement region -   11) extended modified engagement region -   12) extended modified engagement region -   13) braking flank offset -   14) braking flank offset 

1. A sliding cam system of a reciprocating-piston internal combustion engine, comprising a camshaft having at least one sliding cam, which is arranged in a manner which prevents relative rotation but allows axial shifting on at least one axially fixed base shaft in order to form the camshaft, at least one actuating device for adjusting the sliding cam into different axial positions, the at least one actuating device having at least one actuating pin that is made to engage in at least one shifting groove on a periphery of the sliding cam, the actuating device has a housing fixed to the engine and the shifting groove is machined into a top circle surface of the sliding cam down to a groove bottom and is of helical design and has an entry region, a shifting region having an accelerating flank and a braking flank, and an exit region for the actuating pin, the shifting groove has an extended engagement region and the extended engagement region at least partially has a material removal from a level of the top circle surface in a direction of the groove bottom.
 2. The sliding cam system as claimed in claim 1, wherein there are a plurality of shifting grooves and each of the shifting grooves is assigned an extended engagement region.
 3. The sliding cam system as claimed in claim 1, wherein the material removal extends as far as a level of the groove bottom.
 4. The sliding cam system as claimed in claim 1, wherein the extended engagement region corresponds to a peripheral extent of the material removal.
 5. A sliding cam system having two shifting grooves, which are designed as double S grooves, the extended shifting regions for the first shifting grooves amount to between about 145° and about 290° of a cam angle and the extended shifting regions for other of the shifting grooves amount to between about 75° and about 290° of a cam angle.
 6. The sliding cam system as claimed in claim 1, wherein the extended engagement regions correspond to complete sliding cam peripheries minus the shifting regions.
 7. The sliding cam system as claimed in claim 1, wherein the braking flanks of the shifting regions are offset outward into walls of the shifting grooves. 